Due to decreasing prices and improving performance of computer systems, the number of computers in use is rapidly increasing. Furthermore, more and more computers are being coupled to computer networks to provide access to computing resources around the world. Consumer computer systems are typically coupled to a network using a network interface card. FIG. 1 illustrates a typical network interface card 100 coupled to a network 110. Network interface card 100 includes a network controller 103, a transceiver 105, transmit magnetics 107, and receive magnetics 109. Network controller can be for example an Ethernet controller, a FDDI controller or a token ring controller. For clarity, the examples presented herein use Ethernet controllers and Ethernet networks. However the principles of the present invention can be used with other types of network controllers and other types of networks. Network interface cards typically also includes a network connector (not shown), such as an RJ 45 connector.
Network controller 103 communicates with the computer system and converts data from the computer system for transmission on network 110. Furthermore, network controller 103 converts data on network 110 for use by the computer system. Specifically, network controller 103 is coupled to transceiver 105, which converts data signals from network controller 103 to the proper voltage and timing of network 110. Specifically transceiver 105 generates outgoing data on a pair of differential transmit lines T+ and T−. For clarity, lines and signals on the lines are given the same reference names. Thus, transmit signal T+ is on transmit line T+. Transmit lines T+ and T− are coupled to transmit magnetics 107. Transmit magnetics 107 provides DC isolation between transceiver 105 and network 110. For example, magnetics may be used to limit electrical connections only within certain frequency ranges, such as 10 Khz to 100 Mhz. Furthermore, the magnetics serve as a protective barrier against electromagnetic interference from power supplies, telephone ring signals, electrostatic discharges, and lightning strikes. Typically, the placement of transceiver 105 with respect to transmit magnetics 107 are carefully defined by the vendors of transceiver 105 and transmit magnetics 107. Specifically, vendors guarantee proper data signal characteristics only when transceiver 105 and transmit magnetics 107 are directly coupled and in close proximity on a single printed circuit board. Transmit magnetics 107 are coupled to network 110 by a pair of differential transmit lines T_NET+ and T_NET−. Data from network 110 are received on a pair of differential receive lines R_NET+ and R_NET−. Receive magnetics 109 provides DC isolation between differential receive lines R_NET+ and R_NET− and differential receives lines R+ and R−, which are coupled to transceiver 105.
With the rapid evolution of computer technology, prices on all facets of computer systems including computer networking has fallen drastically. Thus, many facets of computer networking have been adapted for use in other industries such as telecommunications. Telecommunication equipment generally must conform to predefined standards. For example, networking gear used in telecommunications are usually mounted in racks that include a back plane. The racks allow a front module and a rear transition module to be coupled through the back plane. Furthermore, telecommunications equipment typically must provide input/output connections on the rear transition module. The advantage of splitting the network interface onto a front module and a rear transition module is that the front module can be easily replaced without requiring the rewiring of the input/output connections residing on the rear transition module.
FIG. 2 illustrates a typical network interface for a telecommunications rack 200. The mechanical portions of telecommunications rack 200, such as the rack sides, board guides, and network connectors are omitted for clarity. Telecommunications rack 200 includes a back plane 230 having connectors 232 and 234. Connector 232 is configured to connect to a front module 210. Connector 234 is configured to connect to a rear transition module 220. In general, connector 232 and connector 234 share a set of pins and thus couples front module 210 to rear transition module 220. Although not shown, back plane 230 typically includes multiple slots for multiple front modules and multiple rear transition modules. In addition, most embodiments of rack 200 and back plane 230 have multiple connectors in each slot. Thus a front module can be coupled to a rear transition module using multiple connectors.
As explained above, vendors of transceiver 105 require that transceiver 105 and transmit magnetics 107 be directly coupled and in close proximity on a single printed circuit board. Thus, as shown in FIG. 2, both transceiver 105 and transmit magnetics 107 are placed on rear transition module 220. For clarity, similar elements in different figures are referenced by the same reference numerals. Transceiver 105 is coupled to transmit magnetics 107 by differential transmit lines T+ and T−. Transmit magnetics 107 are coupled to a network (not shown) using differential transmit lines T_NET+ and T_NET−. Receive magnetics 109 are also placed on rear transition module 220 and coupled to transceiver 105 by differential receive lines R+ and R−. Receive magnetics 109 receive incoming network data on differential receive lines R_NET+ and R_NET−. Generally differential transmit lines T_NET+ and T_NET− and differential receive lines R_NET+ and R_NET− are coupled to a network connector (not shown) on rear transition module 220. The network connector facilitates connection between the network and rear transition module 220. Transceiver 105 is coupled to a connector 223, which can be connected to connecter 234 on back plane 234.
Front module 210 include network controller 103, which is coupled to a connector 215, which can be connected to connector 232 on back plane 230. When connecter 215 of front module 210 is connected to connector 232 of back plane 230 and connector 223 of rear transition module 220 is connected to connector 234 of backplane 230, network controller 103 is coupled to transceiver 105.
As stated above, a major advantage of using a front module and a rear transition module is that the front module can be replaced without rewiring the connections to the rear transition module. However, to realize this advantage, the rear transition board must be more reliable than the front module. Usually reliability of an electronic device is measured using the mean time between failure (MTBF), which represents the average time the part will function before failing in some way. Telecommunications equipment requires very high MTBF for rear transition modules. However, the presence of transceiver 105, which is an active component, on rear transition module 220 lowers the MTBF of rear transition module 220. In general, devices with active components, i.e. components which amplify or generates electronics signals, are rated with a lower MTBF than devices with only passive components, such as transmit magnetics 107 and receive magnetics 109. However, as explained above, most transceiver vendors stipulates that transceiver 105 must be directly coupled to transmit magnetics 107 and that transceiver 105 and transmit magnetics 107 must be in close proximity on a single printed circuit board. Hence, there is a need for a network interface system using multiple boards with one of the boards having a high MTBF.